Sumba Area: Detached Sundaland Terrane and Petroleum Implications

Proceedings, Indonesian Petroleum Association
Thirty-Fifth Annual Convention & Exhibition, May 2011

Sumba Area: Detached Sundaland Terrane and Petroleum Implications

Awang Harun Satyana*, Margaretha E.M. Purwaningsih**
** ConocoPhillips Indonesia

Sumba Island is a terrane situated in the forearc setting of the Neogene-Quaternary Sunda-Banda volcanic arc. Sumba is considered a microcontinent and its origin has been a matter of debate.

There are two main competing hypotheses: (1) provenance from NW Australia or (2) provenance from SE/Eastern Sundaland. We studied various considerations from previous authors and present a new interpretation and synthesis based on multidisciplinary methods including: stratigraphic succession, geochronology-geochemistry of magmatic rocks, paleomagnetism, isotope geology, and Eocene large foraminifera.

The Paleogene stratigraphic succession of Sumba is similar to that of Southern Sulawesi. Extruded magmas display the characteristics of typical island arc environment at the margin of Sundaland. Paleomagnetic data of Sumba show the location of SE/Eastern Sundaland in the Late Cretaceous and has occupied its present position since the Early Miocene. Pb-Nd isotope characteristics of rocks from Sumba show isotopic signatures and affinities with rocks of Sundaland. Sumba contains typical Eocene low-latitude Sundaland fauna of Assilina, Pellatispira, and Biplanispira and no Eocene high-latitude Australian fauna of Lacazinella. We present new consideration on the detachment of Sumba from SE/Eastern Sundaland and its emplacement as continental sliver at its present position through escape tectonics.

Petroleum accumulations occur and are produced from Eastern Indonesian foreland basins related to collision of ‘Australoid’ microcontinents like the Banggai and Bintuni Basins. However, this collision-related petroleum play does not typify the Sumba microcontinent due to the absence of Australian sediments and no collision in its history. Rifted structures, proven to be prolific in Western Western Indonesian basins define the Sumba petroleum potential. Geology of Sumba Island, marine seismic and the presence of petroleum seeps/slicks show positive indications of a petroleum system in Sumba area.

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